Thiol-oxidation reduces the release of amylase induced by β-adrenergic receptor activation in rat parotid acinar cells

Abstract

In parotid acinar cells, the activation of β-adrenergic receptors induces the accumulation of intracellular cAMP, and consequently provokes the exocytotic release of amylase, a digestive enzyme. The cellular redox status plays a pivotal role in regulating various cellular functions. Cellular redox imbalance caused by the oxidation of cellular antioxidants, as a result of oxidative stress, induces significant biological damage. In this study, we examined the effects of diamide, a thioloxidizing reagent, on amylase release by rat parotid acinar cells. In cells treated with diamide, the formation of cAMP and the release of amylase induced by the β-agonist isoproterenol (IPR) were partially reduced. The inhibitory effect of diamide on the IPR-induced release of amylase could be abrogated by reduced glutathione or dithiothreitol. Diamide had no effect on the amylase release induced by forskolin, an adenylate cyclase activator, or by mastoparan, a heterotrimeric GTPbinding protein activator. In cells treated with diamide, the binding affinity for [ 3 H]DHA, but not the number of binding sites, was reduced. These results suggest that β-adrenergic receptor function is reduced by thiol-oxidation, which inhibits amylase secretion by parotid acinar cells.Reactive oxygen species (ROS) play important roles as cell signaling molecules for normal biological processes. However, excessive generation of ROS and/or impairment of antioxidant defenses that protect cells provoke alterations in cellular homeostasis, oxidative stress, inflammation, aging and the pathogenesis of a variety of diseases such as cancer, asthma, pulmonary hypertension and retinopathy (2,8,12,16). Under conditions of oxidative stress, the thiols in cysteine residues within proteins are the most susceptible target among oxidant-sensitive molecules (4,11,27,32). Cysteine is present in the active sites of many proteins and in protein motifs that function in protein regulation and trafficking, cellular signaling, and control of gene expression (4, 11). Therefore, modifications to thiols in proteins potentially affect the protein functions, and the degree of disruption depends on the importance of the cysteine residue(s) in carrying out those functions. Diamide (diazenedicarboxylic acid bis (N,N'-diamethylamide)) is an oxidizing compound. Because diamide easily penetrates cell membranes and reacts quickly and specifically with intracellular thiols (both low-molecular-mass thiols and protein sulfhydryls) without producing free radicals or other ROS (6,13,23,24), this compound is conveniently used for studies of thiol-oxidation. In salivary glands, it has been supposed that ROS are involved in the impairment of functions caused by inflammation, drugs, ionizing irradiation and ag-

Effect of Oxidative Stress on Secretory Function in Salivary Gland Cells

“…In rat parotid acinar cells, the thiol-oxidizing compound diamide has been demonstrated to reduce the binding affinity of -adrenergic receptors for ligands and consequently inhibit IPR-induced amylase release (Guo et al, 2010). Diamide had also no effect on mastoparanor forskolin-induced amylase release and failed to inhibit IPR-induced amylase release in the presence of thiol-reducing reagents, dithiothreitol and GSH, as well as ethacrynic acid described in this paper.…”

Adverse effects of Microcystis aeruginosa exudates on the filtration, digestion, and reproduction organs of benthic bivalve Corbicula fluminea

“…The digestive gland is the main detoxification organ of C. fluminea 41 , 70 , activation of CYP450 and GST in the organ after MaE exposure suggested organic compound detoxification system was stimulated by MaE treatment. Although the function of amylase is catalyzing starch hydrolysis and providing energy, its significant positive correlation with CYP450/GST suggests C. fluminea may increase its resistance to MaE toxicity by supporting the detoxification system through promoting the digestion function 71 – 73 .…”

Particulate Matter Promotes In Vitro Receptor‐Recognizable Low‐Density Lipoprotein Oxidation and Dysfunction of Lipid Receptors

“…The exact nature of PM/SR interactions and the mechanisms involved in the observed changes in receptor functionality remains to be described. These interactions may be related to receptor downregulation , direct physical PM/receptor interaction, or secondary to PM‐related oxidative potential, as described under different conditions .…”